In order to ensure the ground's bearing capacity of soil for constructing a structure, linear piles including steel piles, PHC piles, etc. are generally constructed.
However, these conventional piles have the following problems.
First, the ground is not formed to have a generally constant bearing capacity of soil and there exist layers (supporting layers such as a weak stratum, a rock layer, and so on) having different bearing capacities of soil from each other according to their depths. Despite this, conventional piles have all the same cross sections regardless of the depth, and therefore are not efficient.
Second, because a boring hole should be formed with the same diameter even in the deep depth, boring equipment is overloaded.